Solar cell and method of manufacturing the same

ABSTRACT

Disclosed is a solar cell including a semiconductor substrate, and a dopant layer disposed over one surface of the semiconductor substrate and having a crystalline structure different from that of the semiconductor substrate, the dopant layer including a dopant. The dopant layer includes a plurality of semiconductor layers stacked one above another in a thickness direction thereof, and an interface layer interposed therebetween. The interface layer is an oxide layer having a higher concentration of oxygen than that in each of the plurality of semiconductor layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean PatentApplication No. 10-2015-0093401, filed on Jun. 30, 2015 in the KoreanIntellectual Property Office, the disclosures of which are incorporatedherein by reference.

BACKGROUND

1. Technical Field

Embodiments of the present inventive concept relate to a solar cell anda method of manufacturing the same, and more particularly, to a solarcell, which includes a dopant layer having a crystalline structuredifferent from that of a semiconductor substrate, and a method ofmanufacturing the same.

2. Description of the Related Art

Recently, due to depletion of existing energy resources, such as oil andcoal, interest in alternative sources of energy to replace the existingenergy resources is increasing. Most of all, solar cells are popularnext generation cells to convert sunlight into electrical energy.

Solar cells may be manufactured by forming various layers and electrodesbased on some design. The efficiency of solar cells may be determined bythe design of the various layers and electrodes. In order for solarcells to be commercialized, there is a demand for solar cells, whichhave the maximized efficiency and minimized manufacturing costs.

SUMMARY OF THE INVENTIVE CONCEPT

Therefore, the embodiments of the present inventive concept have beenmade in view of the above problems, and it is an object of the presentinventive concept to provide a solar cell having excellent efficiencyand high productivity and a method of manufacturing the same.

In accordance with one aspect of the present inventive concept, theabove and other objects can be accomplished by the provision of a solarcell including a semiconductor substrate, and a dopant layer disposedover one surface of the semiconductor substrate and having a crystallinestructure different from that of the semiconductor substrate, the dopantlayer including a dopant. The dopant layer includes a plurality ofsemiconductor layers stacked one above another in a thickness directionthereof, and an interface layer interposed therebetween. The interfacelayer is an oxide layer having a higher concentration of oxygen thanthat in each of the plurality of semiconductor layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent inventive concept will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a sectional view illustrating a solar cell in accordance withan embodiment of the present inventive concept;

FIG. 2 is a plan view of the solar cell illustrated in FIG. 1;

FIGS. 3A to 3I are sectional views illustrating a method ofmanufacturing a solar cell in accordance with an embodiment of thepresent inventive concept;

FIG. 4 is a graph illustrating the concentrations of a dopant and oxygenmeasured before heat treatment is performed;

FIG. 5 is a view illustrating examples of a plurality of semiconductorlayers of a solar cell in accordance with various alternativeembodiments of the present inventive concept;

FIG. 6 is a graph illustrating the concentrations of a dopant and oxygenmeasured after heat treatment is performed;

FIG. 7 is a sectional view illustrating a solar cell in accordance withanother embodiment of the present inventive concept;

FIG. 8 is a sectional view illustrating a solar cell in accordance withanother embodiment of the present inventive concept; and

FIG. 9 is a sectional view illustrating a solar cell in accordance witha further embodiment of the present inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinventive concept, examples of which are illustrated in the accompanyingdrawings. However, it will be understood that the present inventiveconcept should not be limited to the embodiments and may be modified invarious ways.

In the drawings, to clearly and briefly explain the embodiments of thepresent inventive concept, illustration of elements having no connectionwith the description is omitted, and the same or extremely similarelements are designated by the same reference numerals throughout thespecification. In addition, in the drawings, for more clear explanation,the dimensions of elements, such as thickness, width, and the like, areexaggerated or reduced, and thus the thickness, width, and the like ofthe embodiments of the present inventive concept are not limited to theillustration of the drawings.

In the entire specification, when an element is referred to as“including” another element, the element should not be understood asexcluding other elements so long as there is no special conflictingdescription, and the element may include at least one other element. Inaddition, it will be understood that, when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. On the other hand, when an element such as a layer, film,region or substrate is referred to as being “directly on” anotherelement, this means that there are no intervening elements therebetween.

Hereinafter, a solar cell and a method of manufacturing the same inaccordance with the embodiments of the present inventive concept will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view illustrating a solar cell in accordance withan embodiment of the present inventive concept, and FIG. 2 is a planview of the solar cell illustrated in FIG. 1. In FIG. 2, illustration isfocused on a semiconductor substrate and electrodes.

Referring to FIG. 1, the solar cell, designated by reference numeral100, includes a semiconductor substrate 110, and a dopant layer DLincluding a dopant, the dopant layer DL being disposed over one surfaceof the semiconductor substrate 110 and having a crystalline structuredifferent from that of the semiconductor substrate 110. The dopant inthe dopant layer DL may be of the same conductive type as that of thesemiconductor substrate 110, and may be included at a higher dopingconcentration than that in the semiconductor substrate 110, or may be ofa conductive type different from that of the semiconductor substrate110. The dopant layer DL may configure conductive areas 20 and 30, whichare connected to electrodes 42 and 44, like an emitter area or a backsurface field area, or may configure a field area 50 (FIG. 9) that isnot connected to the electrodes 42 and 44. The conductive areas 20 and30 may include a first conductive area 20 of a first conductive type,and a second conductive area 30 of a second conductive type. Theelectrodes 42 and 44 include a first electrode 42 connected to the firstconductive area 20 and a second electrode 44 connected to the secondconductive area 30. The field area 50 may not be provided in someembodiments.

In one example, in the present embodiment, the solar cell 100 mayinclude the first conductive area 20, which is disposed over one surfaceof the semiconductor substrate 110 and is of the first conductive type,and the second conductive area 30, which is disposed over the othersurface of the semiconductor substrate 110 and is of the secondconductive type, and the dopant layer DL may be the first conductivearea 20. In addition, the field area 50 is not separately provided. Thiswill be described below in more detail.

The semiconductor substrate 110 may be formed of crystallinesemiconductors including a single semiconductor material (e.g. group-IVelements). In one example, the semiconductor substrate 110 may be formedof monocrystalline or polycrystalline semiconductors (e.g.monocrystalline or polycrystalline silicon). In particular, thesemiconductor substrate 110 may be formed of monocrystallinesemiconductors (e.g. a monocrystalline semiconductor wafer, and morespecifically, a semiconductor silicon wafer). When the semiconductorsubstrate 110 is formed of monocrystalline semiconductors (e.g.monocrystalline silicon), the solar cell 100 may achieve excellentelectrical properties because the solar cell 100 is based on thesemiconductor substrate 110 formed of monocrystalline semiconductors,which have few defects attributable to their high crystallinity.

The front surface and/or the back surface of the semiconductor substrate110 may be subjected to texturing so as to form protrusions thereon. Inone example, the protrusions may take the form of pyramids havingirregular sizes, and the outer surface of the protrusions may beconfigured by (111) faces of the semiconductor substrate 110. When theprotrusions are formed on, for example, the front surface of thesemiconductor substrate 110 via texturing so that the roughness of thefront surface is increased, the reflectance of light introduced through,for example, the front surface of the semiconductor substrate 110 may bereduced. Accordingly, the quantity of light, which reaches a pn junctionformed by a base area 10 and the first or second conductive area 20 or30, may be increased, which may minimize the loss of light. The presentembodiment illustrates the protrusions formed on the front surface ofthe semiconductor substrate 110. In particular, because the frontsurface of the semiconductor substrate 110 is provided with theprotrusions and the back surface of the semiconductor substrate 110 issubjected to mirror surface grinding, the reflection of light may beminimized on the front surface, into which a relatively large quantityof light is introduced, and the first conductive area 20 may be stablyformed on the back surface. However, the embodiment of the presentinventive concept is not limited thereto. Thus, protrusions may beformed on both the front surface and the back surface of thesemiconductor substrate 110. Alternatively, no protrusions may be formedon both the front surface and the back surface of the semiconductorsubstrate 110.

In the present embodiment, the semiconductor substrate 110 includes thebase area 10 in which a first or second conductive dopant is doped at arelatively low concentration so that the base area 10 is of the first orsecond conductive type. At this time, the base area 10 of thesemiconductor substrate 110 may have a lower doping concentration,higher resistance, or lower carrier concentration than one of the firstand second conductive areas 20 and 30, which is of the same conductivetype as that of the base area 10.

The first conductive area 20 of the first conductive type may bedisposed over one surface (e.g. the back surface) of the semiconductorsubstrate 110. In one example, a tunneling layer 22 may be formed overthe semiconductor substrate 110, and the first conductive area 20 may beformed over the tunneling layer 22.

In one example, the tunneling layer 22 may be formed so as to come intocontact with the back surface of the semiconductor substrate 110, whichmay result in a simplified configuration and improved tunneling effects.At this time, the tunneling layer 22 may be formed throughout the backsurface of the semiconductor substrate 110. Here, the expression “formedthroughout the surface” includes the meaning of being physicallycompletely formed over the entire surface as well as the meaning ofbeing formed so as to inevitably exclude a portion of the surface.Thereby, the tunneling layer 22 may be easily formed because a separatepatterning process is not required. However, the embodiment of thepresent inventive concept is not limited thereto.

The tunneling layer 22 may serve as a barrier for electrons and holes,thereby preventing minority carriers from passing therethrough andallowing only majority carriers, which accumulate at a portion adjacentto the tunneling layer 22 and thus have a given amount of energy ormore, to pass therethrough. At this time, the majority carriers, whichhave the given amount of energy or more, may easily pass through thetunneling layer 22 owing to tunneling effects. In addition, thetunneling layer 22 may serve as a diffusion barrier, which prevents thedopant of the conductive areas 20 and 30 from diffusing to thesemiconductor substrate 110. The tunneling layer 22 may comprise variousmaterials to enable the tunneling of the majority carriers. In oneexample, the tunneling layer 22 may comprise oxides, nitrides,semiconductors, and conductive polymers. In particular, the tunnelinglayer 22 may be a silicon oxide layer comprising a silicon oxide. Thisis because the silicon oxide layer has excellent passivation and thusensures easy tunneling of carriers.

In order to achieve sufficient tunneling effects, the thickness of thetunneling layer 22 may be less than the thicknesses of the first andsecond passivation films 24 and 34 and the thickness of the first orsecond conductive area 20 or 30. In one example, the thickness of thetunneling layer 22 may be 2 nm or less, for example, within a range from0.1 nm to 1.5 nm (more specifically, within a range from 0.5 nm to 1.5nm). When the thickness of the tunneling layer 22 exceeds 2 nm, smoothtunneling does not occur, and consequently, the efficiency of the solarcell 100 may be deteriorated. When the thickness of the tunneling layer22 is below 0.1 nm, it may be difficult to form the tunneling layer 22having the desired quality. Accordingly, in order to ensure that thetunneling layer 22 exerts sufficient effects or have desired or certaincharacteristics, the thickness of the tunneling layer 22 may be within arange from 0.1 nm to 1.5 nm (more specifically, within a range from 0.5nm to 1.5 nm). However, the embodiment of the present inventive conceptis not limited thereto, and the thickness of the tunneling layer 22 mayhave any of various values.

The first conductive area 20 may include a first conductive dopant, andthus may be of the first conductive type. In one example, the firstconductive area 20 may be formed so as to come into contact with thetunneling layer 22, which may simplify the configuration of the solarcell 100 and maximize the tunneling effects of the tunneling layer 22.However, the embodiment of the present inventive concept is not limitedthereto.

The first conductive area 20 may comprise the same semiconductormaterial as the semiconductor substrate 110 (more specifically, a singlesemiconductor material, for example, silicon). As such, the firstconductive area 20 may have properties similar to the semiconductorsubstrate 110, and thus may minimize a difference in properties that mayoccur when the first conductive area 20 and the semiconductor substrate110 comprise different semiconductor materials. However, because thefirst conductive area 20 is formed over the semiconductor substrate 110separately from the semiconductor substrate 110, the first conductivearea 20 may have a crystalline structure different from that of thesemiconductor substrate 110, in order to be easily formed over thesemiconductor substrate 110.

For example, the first conductive area 20 may be formed by dopingamorphous semiconductors, microcrystalline semiconductors, orpolycrystalline semiconductors (e.g. amorphous silicon, microcrystallinesilicon, or polycrystalline silicon), which may be easily manufacturedvia various methods, such as deposition, with a first conductive dopant.In particular, the first conductive area 20 may comprise polycrystallinesemiconductors (e.g. polycrystalline silicon). As such, the firstconductive area 20 may have excellent electrical conductivity, thusensuring the smooth movement of carriers, and may cause the tunneling ofcarriers to occur efficiently in the tunneling layer 22, which is formedof, for example, an oxide. In particular, because polycrystallinesemiconductors have a low deposition rate, the effect of increasing therate of deposition of the first conductive area 20 or the dopant layerDL may be magnified.

In the present embodiment, the first conductive area 20, which is thedopant layer DL, includes a plurality of semiconductor layers 201 and202 stacked one above another in a thickness direction over thesemiconductor substrate 110 with an interface layer 204 interposedtherebetween. In one example, the present embodiment illustrates thatthe first conductive area 20 includes a single interface layer 204, anda first layer 201 and a second layer 202 disposed with the interfacelayer 204 interposed therebetween. The following description related tothe first layer 201 or the second layer 202 may be applied to thesemiconductor layers 201 and 202. The interface layer 204 may have adifferent material or composition from that of the first layer 201 andthe second layer 202, thus being distinguished from the first layer 201and the second layer 202. In the present embodiment, the interface layer204 may be configured as an oxide layer, which has a higher oxygenconcentration than that in the first layer 201 and the second layer 202.

More specifically, each of the first layer 201 and the second layer 202may be formed of a semiconductor material doped with a first conductivedopant, and the interface layer 204 may be a semiconductor oxide layerformed via combination of a semiconductor material and oxygen (e.g. asilicon oxide layer when the semiconductor material is silicon).

The interface layer 204 may be configured as a surface, which isorthogonal to the thickness direction of the semiconductor substrate110, and may be formed so as to come into contact with the semiconductorlayers 201 and 202 adjacent thereto (i.e. in the present embodiment, thefirst layer 201 and the second layer 202). More specifically, onesurface of the interface layer 204 may wholly come into contact with thefirst layer 201, and the other surface of the interface layer 204 maywholly come into contact with the second layer 202. In the presentembodiment, after the semiconductor layers 201 and 202 are formed usingdifferent process conditions so as to have different properties (inparticular, different doping concentrations), the semiconductor layers201 and 202 are subjected to heat treatment so as to form the firstconductive area 20. In one example, one or one group of thesemiconductor layers 201 and 202 may be formed so as to include a firstconductive dopant and the other one or the other group may be formed soas not to include the first conductive dopant, and then the firstconductive dopant may wholly diffuse in a heat treatment process,whereby the first conductive area 20 may be formed. At this time, a thinnative oxide layer is formed to configure the interface layer 204between the semiconductor layers 201 and 202 because process conditions,properties and the like change when the semiconductor layers 201 and 202are formed. A detailed manufacturing process will be described later indetail with reference to FIGS. 3A to 3I.

The concentration of oxygen in the interface layer 204 may be higherthan the concentration of oxygen in each of the first layer 201 and thesecond layer 202, and may be lower than the concentration of oxygen inthe tunneling layer 22. This is because the interface layer 204 is anative layer generated inartificially or naturally in the manufacturingprocess, and the tunneling layer 22 is an artificial layer formed byinjecting oxygen.

In one example, the concentration of oxygen in the interface layer 204may be at least 1.5 times the concentration of oxygen in each of thefirst layer 201 and the second layer 202. This is because the interfacelayer 204 may require a concentration of oxygen of at least 1.5 timesthat in each of the first layer 201 and the second layer 202 in order tobe detected as an oxide layer, which has a different constituentmaterial or composition from that of the first layer 201 and the secondlayer 202 and thus is distinguished from the first layer 201 and thesecond layer 202. More specifically, the concentration of oxygen in theinterface layer 204 may be within a range from 2 times to 10 times theconcentration of oxygen in each of the first layer 201 and the secondlayer 202. In addition, because the concentration of oxygen in thetunneling layer 22 may be approximately 100 times the concentration ofoxygen in each of the first layer 201 and the second layer 202, theconcentration of oxygen in the tunneling layer 22 may be within a rangefrom 10 times to 50 times the concentration of oxygen in the interfacelayer 204. The concentration of oxygen is limited to the range that mayappear in the tunneling layer 22, which is formed in the depositionprocess for forming the oxide layer, and the interface layer 204, whichis a native oxide layer. However, the embodiment of the presentinventive concept is not limited thereto, and the concentration ofoxygen in the interface layer 204 may change according to, for example,process conditions in the process of manufacturing the first conductivearea 20, which is the dopant layer DL, the constituent materials of thetunneling layer 22, and process conditions in the process ofmanufacturing the tunneling layer 22.

The thickness of the interface layer 204 may be less than the thicknessof each of the first layer 201 and the second layer 202, and may beequal to or less than the thickness of the tunneling layer 22. This isbecause the interface layer 204 is a native layer (or a naturallygenerated) generated in the manufacturing process, and the first layer201, the second layer 202, and the tunneling layer 22 are layersartificially formed so as to have appropriate thicknesses.

In particular, the thickness of the interface layer 204 may be less thanthe thickness of the tunneling layer 22. This is because the tunnelinglayer 22 is thin, but is artificially grown, whereas the interface layer204 is a native layer. In one example, the ratio of the thickness of thetunneling layer 22 to the thickness of the interface layer 204 may bewithin a range from 1:0.1 to 1:0.8 (e.g. within a range from 1:0.3 to1:0.6). This thickness range may ensure that the interface layer 204causes no great deterioration in the properties of the first conductivearea 20.

In one example, the thickness of the interface layer 204 may be 2 nm orless (more specifically, 1 nm or less, for example, within a range from0.2 nm to 1 nm). This thickness may be realized in a native oxide layer.In addition, the thickness of the first layer 201 or the second layer202 may be within a range from 20 nm to 500 nm. When the thickness ofthe first layer 201 or the second layer 202 is below 20 nm, the processtime for forming the first conductive area 20 may be increased and theforming process may be complicated because it is difficult to impart thefirst conductive area 20 with sufficient thickness, or it is necessaryto increase the number of the semiconductor layers 201 and 202. When thethickness of the first layer 201 or the second layer 202 exceeds 500 nm,the thickness of the first conductive area 20 is excessively increased,and consequently, the process time may be increased and the process maybe complicated. However, the embodiment of the present inventive conceptis not limited thereto, and the thickness of the interface layer 204,the thicknesses of the first layer 201 and the second layer 202, and thelike may have various values.

FIG. 1 illustrates that the first layer 201 and the second layer 202have the same thickness or similar thicknesses (e.g. thicknesses havinga difference within 10%). As such, the interface layer 204 may be spacedapart from the surface of the first conductive area 20 by a distancewithin a range from 40% to 60% of the total thickness of the firstconductive area 20. Thereby, in the manufacturing process, the firstconductive dopant, which is included in any one semiconductor layeramong the semiconductor layers 201 and 202, may effectively diffuse tothe other semiconductor layer, which includes no first conductivedopant.

In another example, the difference between the thicknesses of the firstlayer 201 and the second layer 202 may be 10% or more. This is because aspecific semiconductor layer may be formed so as to be thick or thin inconsideration of the process time, the uniform diffusion of the firstconductive dopant, and the like. This will be described in more detailwith regard to the method of manufacturing the solar cell.

In the present embodiment, the interface layer 204 may notify that thefirst conductive area 20, which is the dopant layer DL, has beenmanufactured by a simplified manufacturing process. In addition, whenthe interface layer 204 is present in the first conductive area 20,which is configured as an oxide layer, the interface layer 204 may serveas a barrier for preventing an excessively great quantity of the firstconductive dopant from diffusing. Thereby, it is possible to prevent thefirst conductive dopant from passing through the tunneling layer 22,thereby diffusing to the semiconductor substrate 110. In particular,when the tunneling layer 22 is made thin in order to increase theprobability of tunneling, the first conductive dopant may diffuse to theinside of the semiconductor substrate 110, which is problematic. Thisproblem may be prevented when the interface layer 204 is provided insidethe first conductive area 20 so as to prevent the first conductivedopant from diffusing too far.

The present embodiment illustrates that the first conductive area 20,which is the dopant layer DL, includes one interface layer 204 and twosemiconductor layers 201 and 202 (i.e. the first layer 201 and thesecond layer 202) coming into contact with both surfaces of theinterface layer 204. As such, the first conductive area 20 may be formedso as to have a simplified structure. However, the embodiment of thepresent inventive concept is not limited thereto. Thus, in analternative embodiment, the first conductive area 20 may include aplurality of interface layers 204 (i.e. two or more interface layers204), and three or more semiconductor layers 201 and 202, which aredisposed with the respective interface layers 204 interposedtherebetween. This will be described later in detail with reference toFIG. 5.

In the present embodiment, the first conductive area 20 is formedseparately from the semiconductor substrate 110, which may reducedefects or deterioration in open-circuit voltage caused when a dopedarea is formed inside the semiconductor substrate 110. Thereby, theopen-circuit voltage of the solar cell 100 may be increased.

The second conductive area 30, which is of the second conductive type,may be disposed on the other surface (e.g. the front surface) of thesemiconductor substrate 110. In one example, in the present embodiment,the second conductive area 30 may be configured as a doped area, whichis formed by doping a portion of the semiconductor substrate 110 with asecond conductive dopant. As such, the base area 10 and the secondconductive area 30 may have the same crystalline structure and maycomprise the same semiconductor material as the semiconductor substrate110, but may be of different conductive types or may have differentdoping concentrations from each other. Specifically, when the base area10 is of the first conductive type, the base area 10 and the secondconductive area 30 are of different conductive types. When the base area10 is of the second conductive type, the doping concentration in thesecond conductive area 30 is higher than the doping concentration in thebase area 10.

When the base area 10 is of the first conductive type, the firstconductive area 20 of the first conductive type configures a backsurface field area for forming a back surface field (BSF), which is ofthe same conductive type as that of the semiconductor substrate 110 andhas a higher doping concentration than that in the semiconductorsubstrate 110, and the second conductive area 30 configures an emitterarea, which is of a conductive type different from that of the base area10, thus forming a pn junction with the base area 10. As such, thesecond conductive area 30, which configures the emitter area, isdisposed on the front surface of the semiconductor substrate 110, whichmay minimize an optical path of light reaching the pn junction.

However, the embodiment of the present inventive concept is not limitedthereto. In another example, when the base area 10 is of the secondconductive type, the first conductive area 20 configures an emitterarea, and the second conductive area 30 configures a front surface fieldarea for forming a front surface field (FSF), which is of the sameconductive type as that of the semiconductor substrate 110 and has ahigher doping concentration than that in the semiconductor substrate110.

A p-type dopant, which is used as the first or second conductive dopant,may be selected from among group III elements, such as boron (B),aluminum (Al), gallium (Ga) and indium (In), and an n-type dopant may beselected from among group V elements, such as phosphorus (P), arsenic(As), bismuth (Bi) and antimony (Sb). However, the embodiment of thepresent inventive concept is not limited thereto, and any of variousdopants may be used as the first or second dopant.

Here, in the present embodiment, the first conductive area 20, which isformed separately from the semiconductor substrate 110, is disposed onthe back surface of the semiconductor substrate 110, and the secondconductive area 30, which configures a portion of the semiconductorsubstrate 110, is disposed on the front surface of the semiconductorsubstrate 110. When the first conductive area 20, which has acrystalline structure different from that of the semiconductor substrate110, is disposed on the front surface of the semiconductor substrate110, the absorption of light is increased in the first conductive area20, which may reduce the quantity of light reaching the pn junction. Forthis reason, the first conductive area 20 is disposed on the backsurface of the semiconductor substrate 110. However, the embodiment ofthe present inventive concept is not limited thereto. An alternativeembodiment related to this will be described below in detail withreference to FIG. 7.

In addition, the present embodiment illustrates that one of the firstand second conductive areas 20 and 30 (i.e. the first conductive area20) has a crystalline structure different from that of the semiconductorsubstrate 110. However, the embodiment of the present inventive conceptis not limited thereto. An alternative embodiment will be describedlater in more detail with reference to FIG. 8.

An insulation film may be formed throughout the first and secondconductive areas 20 and 30 excluding openings 102 and 104, whichcorrespond to the first and second electrodes 42 and 44. Specifically, afirst passivation film (or anti-reflection film or reflection film) 24may be formed throughout the first conductive area 20 excluding theopenings 102, and the second passivation film (or anti-reflection film)34 may be formed throughout the second conductive area 30 excluding theopenings 104.

The first passivation film 24 and/or the second passivation film 34 maybe configured as a single film or multiple films according to desiredfunctions.

The first passivation film 24, disposed on the back surface of thesemiconductor substrate 110, may include an anti-reflection film orreflection film according to the configuration of the solar cell 100,and/or may include a layer for passivation in order to prevent surfacerecombination, a capping layer for preventing contamination or damage tothe semiconductor substrate 110, or the like.

In one example, the second passivation film 34, disposed on the frontsurface of the semiconductor substrate 110, may include ananti-reflection film, or may be formed of an anti-reflection film. Assuch, the reflectance of light introduced into the front surface of thesemiconductor substrate 110 may be reduced, whereby the quantity oflight reaching the pn junction, formed by the base area 10 and the firstconductive area 20, may be increased. In this way, the short-circuitcurrent of the solar cell 100 may be increased. In addition, the secondpassivation film 34 may additionally include a layer for passivation inorder to prevent surface recombination, or a capping layer forpreventing contamination or damage to the semiconductor substrate 110.

The first passivation film 24 and/or the second passivation film 34 maybe formed of various materials. In one example, the first passivationfilm 24 and/or the second passivation film 34 may be a single film ormultiple films having the form of a combination of two or more filmsselected from among the group of a silicon nitride film, a siliconnitride film containing hydrogen, a silicon oxide film, a silicon oxidenitride film, an aluminum oxide film, MgF₂, ZnS, TiO₂ and CeO₂. However,the embodiment of the present inventive concept is not limited thereto,and of course the first passivation film 24 and/or the secondpassivation film 34 may be formed of various materials.

The first electrode 42 is disposed over (e.g. in contact with) the firstconductive area 20 so as to be electrically connected to the firstconductive area 20. The first electrode 42 may be electrically connectedto the first conductive area 20 through the opening 102 formed in thefirst passivation film 24 (i.e. by penetrating the first passivationfilm 24). Similarly, the second electrode 44 is disposed over (e.g. incontact with) the second conductive area 20 so as to be electricallyconnected to the second conductive area 30. The second electrode 44 maybe electrically connected to the second conductive area 30 through theopening 104 formed in the second passivation film 34 (i.e. bypenetrating the second passivation film 34). The first and secondelectrodes 42 and 44 may comprise various materials (more specifically,metals) and may have various shapes. The shapes of the first and secondelectrodes 42 and 44 will be described in detail with reference to FIG.2.

The plan shape of the first and second electrodes 42 and 44 will bedescribed in detail with reference to FIG. 2.

Referring to FIG. 2, the first and second electrodes 42 and 44 mayinclude a plurality of finger electrodes 42 a and 44 a, which are spacedapart from one another at a constant pitch. Although FIG. 2 illustratesthat the finger electrodes 42 a and 44 a are parallel to one another andare also parallel to the edge of the semiconductor substrate 110, theembodiment of the present inventive concept is not limited thereto. Inaddition, the first and second electrodes 42 and 44 may include bus barelectrodes 42 b and 44 b, which are formed in the direction crossing thefinger electrodes 42 a and 44 a so as to connect the finger electrodes42 a and 44 a to one another. Only one bus bar electrode 42 b or 44 bmay be provided, or a plurality of bus bar electrodes 42 b or 44 b maybe arranged at a larger pitch than the pitch of the finger electrodes 42a and 44 a as illustrated in FIG. 2 by example. At this time, althoughthe width of the bus bar electrodes 42 b and 44 b may be larger than thewidth of the finger electrodes 42 a and 44 a, the embodiment of thepresent inventive concept is not limited thereto. Accordingly, the widthof the bus bar electrodes 42 b and 44 b may be equal to or less than thewidth of the finger electrodes 42 a and 44 a.

When viewing the cross section, both the finger electrode 42 a and thebus bar electrode 42 b of the first electrode 42 may be formed so as topenetrate the first passivation film 24. That is, the opening 102 may beformed so as to correspond to both the finger electrode 42 a and the busbar electrode 42 b of the first electrode 42. In addition, both thefinger electrode 44 a and the bus bar electrode 44 b of the secondelectrode 44 may be formed so as to penetrate the second passivationfilm 34. That is, the opening 104 may be formed so as to correspond toboth the finger electrode 44 a and the bus bar electrode 44 b of thesecond electrode 44. However, the embodiment of the present inventiveconcept is not limited thereto. In another example, the finger electrode42 a of the first electrode 42 may be formed so as to penetrate thefirst passivation film 24 and the bus bar electrode 42 b may be formedover the first passivation film 24. In this case, the opening 102 mayhave a shape corresponding to the shape of the finger electrode 42 a,and may not be formed in a portion at which only the bus bar electrode42 b is located. In addition, the finger electrode 44 a of the secondelectrode 44 may be formed so as to penetrate the second passivationfilm 34 and the bus bar electrode 44 b may be formed over the secondpassivation film 34. In this case, the opening 104 may have a shapecorresponding to the shape of the finger electrode 44 a, and may not beformed in a portion at which only the bus bar electrode 44 b is located.

FIG. 2 illustrates that the first electrode 42 and the second electrode44 have the same plan shape. However, the embodiment of the presentinventive concept is not limited thereto, and, for example, the widthand pitch of the finger electrode 42 a and the bus bar electrode 42 b ofthe first electrode 42 may be different from the width and pitch of thefinger electrode 44 a and the bus bar electrode 44 b of the secondelectrode 44. In addition, the first electrode 42 and the secondelectrode 44 may have different plan shapes, and various otheralternative embodiments are possible.

In the present embodiment, as described above, the first and secondelectrodes 42 and 44 of the solar cell 100 have a given pattern so thatthe solar cell 100 has a bi-facial structure to allow light to beintroduced into the front surface and the back surface of thesemiconductor substrate 110. As such, the quantity of light for use inthe solar cell 100 may be increased, which may contribute to improvementin the efficiency of the solar cell 100. However, the embodiment of thepresent inventive concept is not limited thereto, and the firstelectrode 42 may be formed throughout the back surface of thesemiconductor substrate 110. Various other alternative embodiments arepossible.

In the method of manufacturing the solar cell 100 in accordance with thepresent embodiment, the first conductive area 20, which is the dopantlayer DL, may be formed within a short process time. This will bedescribed in detail with reference to FIGS. 3A to 3I. That the firstconductive area 20 is manufactured by the manufacturing method of thepresent embodiment can be appreciated from the fact that the firstconductive area 20 includes the interface layer 204 as described above.

The method of manufacturing the solar cell 100 will be described indetail with reference to FIGS. 3A to 3I. A detailed description relatedto the content described above will be omitted, and only content notdescribed above will be described in detail.

FIGS. 3A to 3I are sectional views illustrating a method ofmanufacturing a solar cell in accordance with an embodiment of thepresent inventive concept.

First, as illustrated in FIG. 3A, the tunneling layer 22 is formed onthe back surface of the semiconductor substrate 110. The tunneling layer22 may be formed throughout the back surface of the semiconductorsubstrate 110.

Here, the tunneling layer 22 may be formed via, for example, thermalgrowth or deposition (e.g. plasma enhanced chemical vapor deposition(PECVD), atomic layer deposition (ALD) or low pressure chemical vapordeposition (LPCVD)). However, the embodiment of the present inventiveconcept is not limited thereto, and the tunneling layer 22 may be formedvia various other methods. In one example, the tunneling layer 22 may beformed of a silicon oxide layer.

Although FIG. 3A illustrates that the tunneling layer 22 is formed onlyon the back surface of the semiconductor substrate 110, the embodimentof the present inventive concept is not limited thereto. The tunnelinglayer 22 may additionally be formed on the front surface and/or the sidesurface of the semiconductor substrate 110 according to the method offorming the tunneling layer 22. The tunneling layer 22, which is formedon, for example, on the front surface of the semiconductor substrate110, may be removed later in a separate operation (e.g. in a texturingprocess illustrated in FIG. 3D).

Subsequently, as illustrated in FIGS. 3B to 3G, the first conductivearea 20 may be formed over the tunneling layer 22, and a texturingstructure and the second conductive area 30 may be formed on the frontsurface of the semiconductor substrate 110. This will be described inmore detail.

An undoped semiconductor layer 201 a is formed over the tunneling layer22 as illustrated in FIG. 3B, and a doped semiconductor layer 202 a isformed over the undoped semiconductor layer 201 a as illustrated in FIG.3C. A process of forming the undoped semiconductor layer 201 a and aprocess of forming the doped semiconductor layer 202 a may besuccessively performed by changing supply target gas within the sameapparatus. That is, a plurality of semiconductor layers 20 a includingthe undoped semiconductor layer 201 a and the doped semiconductor layer202 a may be formed via in-situ processes.

Here, the semiconductor layers 20 a may be formed via, for example,thermal growth, deposition (e.g. plasma enhanced chemical vapordeposition (PECVD), atomic layer deposition (ALD) or low pressurechemical vapor deposition (LPCVD) (more particularly, LPCVD)). However,the embodiment of the present inventive concept is not limited thereto,and the semiconductor layers 20 a may be formed via various othermethods.

The process of forming the semiconductor layers 20 a including theundoped semiconductor layer 201 a and the doped semiconductor layer 202a (e.g. deposition) is performed at a higher temperature than that ofthe room temperature (e.g. a temperature of 600 degrees Celsius ormore). As such, when changing the gas that is supplied in order to formthe doped semiconductor layer 202 a after the undoped semiconductorlayer 201 a is formed, oxygen gas inside the apparatus is decomposed bythe high temperature, thereby being deposited over the undopedsemiconductor layer 201 a, in which state, the changed gas is supplied,thereby forming the doped semiconductor layer 202 a. Thereby, theinterface layer 204, which is an oxide layer having a relatively highconcentration of oxygen, is provided between the undoped semiconductorlayer 201 a and the doped semiconductor layer 202 a.

For example, when the undoped semiconductor layer 201 a and the dopedsemiconductor layer 202 a are formed via deposition, source gasincluding silicon (e.g. silane (SiH₄)) may be supplied when depositingthe undoped semiconductor layer 201 a, and source gas including silicon(e.g. silane (SiH₄)) and dopant gas including a first conductive dopant(e.g. POCl₃ or B₂H₆) may be supplied when depositing the dopedsemiconductor layer 202 a. Generally, after gas, used for the depositionof the undoped semiconductor layer 201 a, is discharged to the outsideby, for example, purging, the gas to be used for the deposition of thedoped semiconductor layer 202 a is supplied. At this time, becauseoxygen, which is naturally introduced from the outside when a door ofthe apparatus is initially opened in order to introduce thesemiconductor substrate 110 or upon purging, is present inside theapparatus, the oxygen inside the apparatus is deposited over the undopedsemiconductor layer 201 a, thereby forming the interface layer 204, andthen the doped semiconductor layer 202 a is formed over the interfacelayer 204.

At this time, the rate of forming the undoped semiconductor layer 201 a,which includes no first conductive dopant, is greater than the rate offorming the doped semiconductor layer 202 a, which includes the firstconductive dopant. In one example, the rate of forming the undopedsemiconductor layer 201 a may be within a range from 10 nm/min to 20nm/min, and the rate of forming the doped semiconductor layer 202 a maybe within a range from 1 nm/min to 5 nm/min. However, because this ratemay change according to specific conditions of the deposition process,the embodiment of the present inventive concept is not limited thereto.

The undoped semiconductor layer 201 a, the doped semiconductor layer 202a, and the interface layer 204 will be described in more detail withreference to FIG. 4. FIG. 4 is a graph illustrating the concentrationsof a dopant (i.e. the first conductive dopant) and oxygen, measured bysecondary ion mass spectrometry (SIMS) after the semiconductor layers 20a including the undoped semiconductor layer 201 a and the dopedsemiconductor layer 202 a are formed. That is, FIG. 4 is a graphillustrating the concentrations of a dopant and oxygen measured prior toperforming heat treatment.

Referring to FIG. 4, it can be appreciated that a first section S1 inwhich the tunneling layer 22 is located exhibits a higher concentrationof oxygen than that in an inner section S0, which corresponds to theinside of the semiconductor substrate 110. In the first section S1, theconcentration of a dopant has a slightly higher peak than that in theundoped semiconductor layer 201 a. This is because the dopant may becondensed on the tunneling layer 22.

In a second section S2 in which the undoped semiconductor layer 201 a islocated, a portion adjacent to the doped semiconductor layer 202 a has adoping concentration similar to that in the doped semiconductor layer202 a, and the doping concentration is gradually reduced with increasingdistance from the doped semiconductor layer 202 a (in the presentembodiment, with decreasing distance to the semiconductor substrate110). Although the undoped semiconductor layer 201 a is formed viadeposition without a dopant, the deposition is performed at a relativelyhigh temperature. Therefore, the above-described doping profile isattained via the diffusion of dopant when the doped semiconductor layer202 a is deposited.

It can be appreciated that a third section S3 in which the interfacelayer 204 is located has a portion at which the concentration of oxygenis rapidly increased to a high value. Referring to FIG. 4, it can beappreciated that the concentration of oxygen in the interface layer 204is lower than the concentration of oxygen in the tunneling layer 22,higher than the concentration of oxygen in the doped semiconductor layer202 a, and higher than the concentration of oxygen in the undopedsemiconductor layer 201 a. In addition, it can be appreciated that thethickness of the interface layer 204 is less than the thickness of eachof the semiconductor layers 20 a or the tunneling layer 22.

In a fourth section S4 in which the doped semiconductor layer 202 a islocated, the concentration of oxygen is generally low, and the dopingconcentration is relatively high and uniform (e.g. with a differencewithin 30%).

FIG. 4 illustrates that the thickness of the doped semiconductor layer202 a is greater than the thickness of the undoped semiconductor layer201 a. As such, by positioning the doped semiconductor layer 202 a,having a high doping concentration, on a portion connected to the firstelectrode 42, the resistance of the first electrode 42 may be maintainedat a low level even if the first conductive dopant does not smoothlydiffuse due to process errors, etc. In addition, the first conductivedopant included in the doped semiconductor layer 202 a may evenlydiffuse throughout the undoped semiconductor layer 201 a.

In another example, the undoped semiconductor layer 201 a may be thickerthan the doped semiconductor layer 202 a. As such, the process time ofthe process of forming the first conductive area 20 may be reducedbecause the undoped semiconductor layer 201 a, which is formed at arelatively high rate, is made thick and the doped semiconductor layer202 a, which is formed at a relatively low rate, is made thin.

Alternatively, as described above, the thickness of the undopedsemiconductor layer 201 a and the thickness of the doped semiconductorlayer 202 a may be the same as or similar to each other. Various otheralternative embodiments are possible.

FIGS. 3B and 3C illustrate that one undoped semiconductor layer 201 a isfirst formed, and then one doped semiconductor layer 202 a is formed sothat two semiconductor layers 20 a are provided. As such, thesemiconductor layers 20 a include two layers, thus having a simplifiedconfiguration and being easily formed in a simplified process. Inaddition, because the doped semiconductor layer 202 a, having a highdoping concentration, is located on a portion connected to the firstelectrode 42, the resistance of the first electrode 42 may be maintainedat a low level even if the first conductive dopant does not smoothlydiffuse due to process errors, etc. However, the embodiment of thepresent inventive concept is not limited thereto. Various alternativeembodiments will be described in detail with reference to FIG. 5.

FIG. 5 is a view illustrating examples of the semiconductor layers 20 aof the solar cell in accordance with various alternative embodiments ofthe present inventive concept. For clear and simplified description,FIG. 5 illustrates only the portion corresponding to the enlarged circleof FIG. 1.

Referring to (a) of FIG. 5, in one alternative embodiment, after thedoped semiconductor layer 202 a is first formed over the tunneling layer22, the undoped semiconductor layer 201 a is formed. At this time, theinterface layer 204 is formed between the doped semiconductor layer 202a and the undoped semiconductor layer 201 a. The doping concentrationmay be high and consistent in the doped semiconductor layer 202 a formedover the tunneling layer 22, and may be gradually reduced in the undopedsemiconductor layer 201 a with increasing distance from the dopedsemiconductor layer 202 a. In addition, the concentration of oxygen inthe interface layer 204 may be higher than the concentration of oxygenin each of the undoped semiconductor layer 201 a and the dopedsemiconductor layer 202 a and may be lower than the concentration ofoxygen in the tunneling layer 22.

Referring to (b) of FIG. 5, in another alternative embodiment, theundoped semiconductor layer 201 a, the doped semiconductor layer 202 a,and the undoped semiconductor layer 201 a are formed in sequence overthe tunneling layer 22. At this time, the interface layers 204 areformed respectively between the undoped semiconductor layer 201 aadjacent to the tunneling layer 22 and the doped semiconductor layer 202a and between the doped semiconductor layer 202 a and the undopedsemiconductor layer 201 a adjacent to the first passivation film 24. Thedoping concentration may be high and consistent in the dopedsemiconductor layer 202 a, may be gradually reduced in the undopedsemiconductor layer 201 a adjacent to the tunneling layer 22 withincreasing distance from the doped semiconductor layer 202 a anddecreasing distance to the tunneling layer 22, and may be graduallyreduced in the undoped semiconductor layer 201 a adjacent to the firstpassivation film 24 with increasing distance from the dopedsemiconductor layer 202 a and decreasing distance to the firstpassivation film 24. In addition, the concentration of oxygen in eachinterface layer 204 may be higher than the concentration of oxygen ineach of the two undoped semiconductor layers 201 a and the dopedsemiconductor layer 202 a, and may be lower than the concentration ofoxygen in the tunneling layer 22.

Referring to (c) of FIG. 5, in a further alternative embodiment, thedoped semiconductor layer 202 a, the undoped semiconductor layer 201 a,and the doped semiconductor layer 202 a are formed in sequence over thetunneling layer 22. At this time, the interface layers 204 are formedrespectively between the doped semiconductor layer 202 a adjacent to thetunneling layer 22 and the undoped semiconductor layer 201 a and betweenthe undoped semiconductor layer 201 a and the doped semiconductor layer202 a adjacent to the first passivation film 24. The dopingconcentration may be high and even in the two doped semiconductor layers202 a, and may be gradually reduced in the undoped semiconductor layer201 a located between the two doped semiconductor layers 202 a withincreasing distance from the respective doped semiconductor layers 202a. That is, the undoped semiconductor layer 201 a may have a dopingprofile in which the doping concentration is gradually reduced withincreasing distance from the doped semiconductor layer 202 a adjacent tothe tunneling layer 22 and then gradually increased with decreasingdistance to the doped semiconductor layer 202 a adjacent to the firstpassivation film 24. In addition, the concentration of oxygen in eachinterface layer 204 may be higher than the concentration of oxygen ineach of the two doped semiconductor layers 202 a and the undopedsemiconductor layer 201 a, and may be lower than the concentration ofoxygen in the tunneling layer 22.

In accordance with the present alternative embodiment, the number ofundoped semiconductor layers 201 a may be greater than the number ofdoped semiconductor layers 202 a, making the total thickness of undopedsemiconductor layers 201 a greater than the total thickness of dopedsemiconductor layers 202 a. Thus, the process time of the semiconductorlayers 20 a may be reduced by increasing the occupation rate of theundoped semiconductor layer 201 a, which has a fast growth rate. Inaddition, the number of doped semiconductor layers 202 a may be greaterthan the number of undoped semiconductor layers 201 a, so that eachundoped semiconductor layer 201 a is located between two dopedsemiconductor layers 202 a. This may allow the dopant included in thedoped semiconductor layer 202 a to evenly diffuse to the undopedsemiconductor layer 201 a.

In FIG. 5, (b) and (c) illustrate that one of the doped semiconductorlayer 202 a and the undoped semiconductor layer 201 a is formed into twolayers and the other one is formed into a single layer. However, theembodiment of the present inventive concept is not limited thereto, andthe number of the layers 201 a and 202 a are not limited so long as thedoped semiconductor layer 202 a and the undoped semiconductor layer 201a are alternately formed.

In the case where at least one of the doped semiconductor layer 202 aand the undoped semiconductor layer 201 a is provided in a plural numberas described above, the sum of the thicknesses of the dopedsemiconductor layers 202 a or the sum of the thicknesses of the undopedsemiconductor layers 201 a may be within a range from 20 nm to 500 nm.However, the embodiment of the present inventive concept is not limitedthereto, and the doped semiconductor layers 202 a or the undopedsemiconductor layers 201 a may have different thicknesses from thatdescribed above.

In addition, although (a) to (c) of FIG. 5 illustrate that thesemiconductor layers 20 a are formed only on the back surface of thesemiconductor substrate 110, the embodiment of the present inventiveconcept is not limited thereto. The semiconductor layers 20 a mayadditionally be formed on the front surface and/or the side surface ofthe semiconductor substrate 10 according to the manufacturing methodthereof. The semiconductor layers 20 a, which are formed on, forexample, the front surface of the semiconductor substrate 110 and areactually not required, may be removed in a separate following operation(e.g. in a texturing process illustrated in FIG. 3D).

Subsequently, as illustrated in FIG. 3D, the front surface of thesemiconductor substrate 110 may be subjected to texturing so thatprotrusions are formed on the front surface of the semiconductorsubstrate 110. The texturing performed on the surface of thesemiconductor substrate 110 may be wet or dry texturing. Wet texturingmay be performed by dipping the semiconductor substrate 110 into atexturing solution, and has the advantage of a short processing time.Dry texturing is the process of grinding the surface of thesemiconductor substrate 110 using, for example, a diamond grill orlaser, and may entail the disadvantages of a long processing time andthe potential for damage to the semiconductor substrate 110, although itmay be advantageous in that protrusions are formed evenly. In addition,the texturing on the semiconductor substrate 110 may be, for example,reactive ion etching (RIE). As such, in the embodiment of the presentinventive concept, the semiconductor substrate 110 may be subjected totexturing via various methods.

The present embodiment illustrates that, after the semiconductor layers20 a for the formation of the first conductive area 20 are formed, thefront surface of the semiconductor substrate 110 is subjected totexturing, after which the second conductive area 30 is formed oranother layer for the formation of the second conductive area 30 isformed. However, the embodiment of the present inventive concept is notlimited thereto. Accordingly, the process sequence of texturing thefront surface of the semiconductor substrate 110 may be altered invarious ways.

Subsequently, as illustrated in FIG. 3E, a doping layer 300 including asecond conductive dopant is formed on the front surface of thesemiconductor substrate 110 in order to form the second conductive area30. The doping layer 300 may be any of various layers including thesecond conductive dopant. In one example, the doping layer 300 may beformed of phosphorous silicate glass (PSG) or boron silicate glass(BSG). The doping layer 300 formed of phosphorous silicate glass (PSG)or boron silicate glass (BSG) may be easily formed. However, theembodiment of the present inventive concept is not limited as to theconstituent material of the doping layer 300.

Subsequently, as illustrated in FIG. 3F, the first conductive area 20 isformed by diffusing the first conductive dopant in the dopedsemiconductor layer 202 a (FIG. 3E) to the undoped semiconductor layer201 a (FIG. 3E) via heat treatment, and the second conductive area 30 isformed by diffusing the second conductive dopant in the doping layer 300to the semiconductor substrate 110.

More specifically, the first conductive dopant in the dopedsemiconductor layer 202 a diffuses to the undoped semiconductor layer201 a via heat treatment, such that the first layer 201 and the secondlayer 202, which have similar doping concentrations (e.g. dopingconcentrations having a difference within 30%), are formed with theinterface layer 204 interposed therebetween. At this time, because theconcentration of oxygen is not greatly changed even if heat treatment isperformed, the interface layer 204 having a relatively highconcentration of oxygen is maintained between the first layer 201 andthe second layer 202.

The heat treatment process may be performed in any of various heattreatment apparatuses, and in one example, may be performed at atemperature of 900 degrees Celsius or more (e.g. a temperature within arange from 900 degrees Celsius to 1300 degrees Celsius). However, theembodiment of the present inventive concept is not limited as to theheat treatment apparatus, the temperature thereof, or the like.

The first layer 201, the second layer 202, and the interface layer 204interposed therebetween, which are formed via heat treatment, will bedescribed in more detail with reference to FIG. 6. FIG. 6 is a graphillustrating the concentrations of a dopant (i.e. a first conductivedopant) and oxygen measured by SIMS in the first layer 201, the secondlayer 202, and the interface layer 204 interposed therebetween afterheat treatment. That is, FIG. 6 is a graph illustrating theconcentrations of the dopant and oxygen measured after heat treatment isperformed.

Referring to both FIGS. 4 and 6, it can be appreciated that theconcentration of oxygen is very similar before and after heat treatmentis performed. Accordingly, the interface layer 204 having a relativelyhigh concentration of oxygen is maintained in a third section S3,between a second section S2 in which the first layer 201 is located anda fourth section S4 in which the second layer 202 is located.

In addition, it can be appreciated that the first layer 201, which isformed as the first conductive dopant diffuses to the undopedsemiconductor layer 201 a after heat treatment, has a dopingconcentration the same as or similar to that in the second layer 202,which corresponds to the doped semiconductor layer 202 a after heattreatment. Thereby, it can be appreciated that the entire firstconductive area 20 has a consistent doping concentration after heattreatment.

In the present embodiment, both the first and second conductive areas 20and 30 are subjected to heat treatment in a single process, whichsimplifies a heat treatment process. However, the embodiment of thepresent inventive concept is not limited thereto, and the first andsecond conductive areas 20 and 30 may be subjected to heat treatment indifferent processes. In addition, the heat treatment process of formingat least one of the first and second conductive areas 20 and 30 may benot required, and at least one of the first and second conductive areas20 and 30 may be formed via any high-temperature process during themanufacture of the solar cell 100.

The present embodiment illustrates that the second conductive area 30 isformed by forming the doping layer 300 and then performing heattreatment on the doping layer 300. However, the embodiment of thepresent inventive concept is not limited thereto, and the secondconductive area 30 may be formed via any of various known methods. Inone example, various methods, such as ion implantation, thermaldiffusion using heat treatment in the state in which gas includingdopant is used, and laser doping, may be applied.

Subsequently, as illustrated in FIG. 3G, the doping layer 300 may beremoved. In one example, the doping layer 300 may be easily removedusing an etching solution (e.g. diluted hydrofluoric acid (DHF)).

Subsequently, as illustrated in FIG. 3H, insulation films are formed onthe front surface and the back surface of the semiconductor substrate110. That is, the first passivation film 24 is formed on the backsurface of the semiconductor substrate 110, and the second passivationfilm 34 is formed on the front surface of the semiconductor substrate110.

More specifically, the first passivation film 24 is formed throughoutthe back surface of the semiconductor substrate 110, and the secondpassivation film 34 is formed throughout the front surface of thesemiconductor substrate 110. The first passivation film 24 and thesecond passivation film 34 may be formed via any of various methods,such as vacuum deposition, chemical vapor deposition, spin coating,screen printing, or spray coating. The sequence of forming the firstpassivation film 24 and the second passivation film 34 is not limited.

Subsequently, as illustrated in FIG. 3I, the first and second electrodes42 and 44, which are connected respectively to the first and secondconductive areas 20 and 30, are formed.

In one example, the first and second openings 102 and 104 are formed inthe first and second passivation films 24 and 34 via patterning, andthereafter are filled with the first and second electrodes 42 and 44. Atthis time, the first and second openings 102 and 104 may be formed viaany of various methods, such as laser ablation using a laser, or etchingusing an etching solution or etching paste. In addition, the first andsecond electrodes 42 and 44 may be formed via any of various methods,such as plating or deposition.

In another example, after a paste for the formation of the first andsecond electrodes 42 and 44 may be applied on the first and secondpassivation films 24 and 34 via screen printing or the like, forexample, fire-through phenomenon or laser firing contact may be used inorder to form the first and second electrodes 42 and 44 having theabove-described shape. In this case, because the first and secondopenings 102 and 104 are formed when the first and second electrodes 42and 44 are formed, no process of forming the first and second openings102 and 104 is added.

In the present embodiment, after the semiconductor layers 20 a includingthe undoped semiconductor layer 201 a, which is formed at a relativelyhigh rate, and the doped semiconductor layer 202 a, which includes thefirst conductive dopant, are formed, the first conductive area 20 isformed by diffusing the first conductive dopant included in the dopedsemiconductor layer 202 a to the undoped semiconductor layer 201 a viaheat treatment. Thereby, the first conductive area 20 may be formedwithin a reduced time while maintaining excellent properties, which mayincrease the productivity of the solar cell 100.

On the other hand, unlike the present embodiment, when a single undopedsemiconductor layer 201 a is formed in order to form the firstconductive area 20, it is necessary to perform a separate doping processlater. Such a requirement for an additional process may increase thenumber of processes, thus causing deterioration in the productivity ofthe solar cell 100. In addition, when a single doped semiconductor layer202 a is formed in order to form the first conductive area 20, theprocess time necessary in order to form the doped semiconductor layer202 a to a sufficient thickness may be increased due to the lowdeposition rate. This may deteriorate the productivity of the solar cell100.

Hereinafter, solar cells in accordance with other embodiments of thepresent inventive concept will be described in detail with reference toFIGS. 7 to 9. A detailed description related to parts that are the sameor extremely similar to those of the above description will be omittedbelow and the following description will be focused on different parts.In addition, combinations of the above-described embodiments oralternative embodiments thereof with the following embodiment oralternative embodiments thereof fall within the scope of the embodimentof the present inventive concept.

FIG. 7 is a sectional view illustrating a solar cell in accordance withanother embodiment of the present inventive concept.

Referring to FIG. 7, in the present embodiment, the tunneling layer 22,the first conductive area 20, and the first electrode 42 connected tothe first conductive area 20 are disposed on the front surface of thesemiconductor substrate 110, and the second conductive area 30 and thesecond electrode 44 connected to the second conductive area 30 aredisposed on the back surface of the semiconductor substrate 110. At thistime, the first conductive area 20 may include the first layer 201 andthe second layer 202 disposed with the interface layer 204 interposedtherebetween, and the second conductive area 30 may be a doped area.Although FIG. 7 illustrates that both the front surface and the backsurface of the semiconductor substrate 110 have no protrusions formedvia texturing, the embodiment of the present inventive concept is notlimited thereto. Thus, at least one of the front surface and the backsurface of the semiconductor substrate 110 may have protrusions formedvia texturing.

FIG. 8 is a sectional view illustrating a solar cell in accordance withanother embodiment of the present inventive concept.

Referring to FIG. 8, each of the first and second conductive areas 20and 30 may have a crystalline structure different from that of thesemiconductor substrate 110. When the second conductive area 30 has acrystalline structure different from that of the semiconductor substrate110, another tunneling layer 32 may be provided between the secondconductive area 30 and the semiconductor substrate 110. In this case, adetailed description of the second conductive area 30 and the othertunneling layer 32 will be omitted because the above description relatedto the first conductive area 20 and the tunneling layer 22 may beapplied to the second conductive area 30 and the other tunneling layer32.

In the present embodiment, the other tunneling layer 32 is providedbetween the semiconductor substrate 110 and the second conductive area30, which may maximize passivation effects and ensure the smoothmovement of carriers.

In addition, the semiconductor substrate 110 includes only the base area10 without a separate doped area. In one example, the difference betweenthe highest doping concentration and the lowest doping concentration inthe semiconductor substrate 110 may be 30% or less. At this time, thevalue of 30% or less is given by way of example in order to define thedegree at which a doped area is not formed, and the embodiment of thepresent inventive concept is not limited thereto. Thus, the embodimentof the present inventive concept typically includes all cases in whichthe semiconductor substrate 110 includes no doped area.

In the present embodiment, the open-circuit voltage may be increasedbecause the semiconductor substrate 110 includes no doped area. This isbecause providing the semiconductor substrate 110 with a doped area mayprevent surface recombination.

FIG. 8 illustrates an alteration or modification based on the solar cell100 illustrated in FIG. 1. However, the embodiment of the presentinventive concept is not limited thereto, and any alteration ormodification based on the solar cell 100 illustrated in FIG. 7 fallswithin the scope of the embodiment of the present inventive concept. Inaddition, although an example in which both the front surface and theback surface of the semiconductor substrate 110 have no protrusionsformed via texturing is illustrated, the embodiment of the presentinventive concept is not limited thereto. Thus, at least one of thefront surface and the back surface of the semiconductor substrate 110may have protrusions formed via texturing.

FIG. 9 is a sectional view illustrating a solar cell in accordance witha further embodiment of the present inventive concept.

Referring to FIG. 9, the solar cell 100 in accordance with the presentembodiment may be of a back contact type. That is, the tunneling layer22 may be disposed on the back surface of the semiconductor substrate110, and the first and second conductive areas 20 and 30 may be disposedon the same plane over the tunneling layer 22. Because the first andsecond conductive areas 20 and 30 are formed over the semiconductorsubstrate 110 separately from the semiconductor substrate 110, the firstand second conductive areas 20 and 30 may have a crystalline structuredifferent from that of the semiconductor substrate 110 in order to beeasily formed over the semiconductor layer 110.

For example, the first conductive area 20 may be formed by dopingamorphous semiconductors, microcrystalline semiconductors, orpolycrystalline semiconductors (e.g. amorphous silicon, microcrystallinesilicon, or polycrystalline silicon), which may be easily manufacturedvia various methods, such as deposition, with a first conductive dopant.In particular, the first conductive area 20 may comprise polycrystallinesemiconductors (e.g. polycrystalline silicon). Similarly, the secondconductive area 30 may be formed by doping amorphous semiconductors,microcrystalline semiconductors, or polycrystalline semiconductors (e.g.amorphous silicon, microcrystalline silicon, or polycrystallinesilicon), which may be easily manufactured via various methods, such asdeposition, with a second conductive dopant. In particular, the secondconductive area 30 may comprise polycrystalline semiconductors (e.g.polycrystalline silicon).

In addition, the field area 50 may be formed over the front surface ofthe semiconductor substrate 110 so as to come into contact with thesemiconductor substrate 110. The field area 50 may have the sameconductive type as that of the semiconductor substrate 110, and may havea higher doping concentration than that in the semiconductor substrate110.

In the present embodiment, because the field area 50 is formed over thesemiconductor substrate 110 separately from the semiconductor substrate110, the field area 50 may have a crystalline structure different fromthat of the semiconductor substrate 110 in order to be easily formedover the semiconductor substrate 110. For example, the field area 50 maybe formed by doping amorphous semiconductors, microcrystallinesemiconductors, or polycrystalline semiconductors (e.g. amorphoussilicon, microcrystalline silicon, or polycrystalline silicon), whichmay be easily manufactured via various methods, such as deposition, witha first or second conductive dopant. In particular, the field area 50may comprise polycrystalline semiconductors (e.g. polycrystallinesilicon).

At this time, the field area 50, which is disposed on the front surfaceof the semiconductor substrate 110 and is not connected to theelectrodes 42 and 44, may be a dopant layer DL. In addition, at leastone of the first and second conductive areas 20 and 30 disposed over theback surface of the semiconductor substrate 110 may be a dopant layerDL.

That is, the field area 50 may include a first layer 501, a second layer502, and an interface layer 504 interposed therebetween. The first layer501 may be formed in contact with the semiconductor substrate 110. Adetailed description related to other details of the first layer 501,the second layer 502, and the interface layer 504 will be omittedbecause the above description related to the first layer 201, the secondlayer 202 and the interface layer 204 may be applied to the first layer501, the second layer 502, and the interface layer 504.

In addition, the first and second conductive areas 20 and 30 may includethe first layer 201, the second layer 202, and the interface layer 204interposed therebetween. A detailed description related to the firstlayer 201, the second layer 202, and the interface layer 204 will beomitted because the above description related to the first layer 201,the second layer 202 and the interface layer 204 may be applied thereto.In this case, the first and second conductive areas 20 and 30 may beformed by forming a plurality of semiconductor layers 20 a (FIG. 3C),which include at least an undoped semiconductor layer 201 a (FIG. 3C), afirst or second conductive-type doped semiconductor layer 202 a (FIG.3C) and an interface layer 204, over the tunneling layer 22, andthereafter performing over-doping on a portion of the semiconductorlayers 20 a using a dopant having an opposite, that is, second or first,conductive type and then performing heat treatment. For example, whenattempting to form the first conductive area 20 over a relatively widearea, the semiconductor layers 20 a of a first conductive type may beformed, and thereafter a portion thereof corresponding to the secondconductive area 30 may be subjected to over-doping using a secondconductive dopant. Thereby, because over-doping is performed on arelatively small area, the first and second conductive areas 20 and 30may be formed in a simplified manufacturing process while maintainingexcellent properties thereof.

The present embodiment illustrates that each of the field area 50 andthe first and second conductive areas 20 and 30 includes the first layer501 or 201, the second layer 502 or 202, and the interface layer 504 or204. However, the embodiment of the present inventive concept is notlimited thereto, and any one of the field area 50 and the first andsecond conductive areas 20 and 30 may have the above-describedconfiguration.

As is apparent from the above description, in accordance with theembodiments of the present inventive concept, after a plurality ofsemiconductor layers including an undoped semiconductor layer, which isformed at a relatively high rate, and a doped semiconductor layerincluding a dopant are formed, a conductive area is formed by diffusingthe dopant included in the doped semiconductor layer to the undopedsemiconductor layer via heat treatment. Thereby, the conductive area maybe manufactured within a reduced processing time while maintainingexcellent properties, which may improve the productivity of a solarcell.

The above described features, configurations, effects, and the like areincluded in at least one of the embodiments of the present inventiveconcept, and should not be limited to only one embodiment. In addition,the features, configurations, effects, and the like as illustrated ineach embodiment may be implemented with regard to other embodiments asthey are combined with one another or modified by those skilled in theart. Thus, content related to these combinations and modificationsshould be construed as including in the scope and spirit of theinventive concept as disclosed in the accompanying claims.

What is claimed is:
 1. A solar cell comprising: a single crystallinesemiconductor substrate; an oxide layer disposed on a first surface ofthe single crystalline semiconductor substrate; a conductive areadisposed on the oxide layer and including a first polycrystallinesilicon layer, a second polycrystalline silicon layer and an interfacelayer interposed between the first polycrystalline silicon layer and thesecond polycrystalline silicon layer; a diffusion region on a secondsurface of the single crystalline semiconductor substrate, andconstituting a portion of the single crystalline silicon substrate; afirst passivation on the conductive area and having a plurality of firstopenings; a second passivation on the diffusion region and having aplurality of second openings; a plurality of first electrodes eachconnected to the conductive area through the plurality of firstopenings; and a plurality of second electrodes each connected to thediffusion region through the plurality of second openings, wherein theconductive area has the same conductive type as a conductive type of thesingle crystalline silicon substrate, and wherein the diffusion regionhas a conductive type opposite to the conductive type of the singlecrystalline silicon substrate.
 2. The solar cell according to claim 1,wherein the interface layer is a silicon oxide layer.
 3. The solar cellaccording to claim 1, wherein the interface layer is an oxide layerhaving a higher concentration of oxygen than that in each of the firstand second polycrystalline silicon layers, and wherein the concentrationof oxygen in the interface layer is at least 1.5 times a concentrationof oxygen in each of the first and second polycrystalline siliconlayers.
 4. The solar cell according to claim 3, wherein theconcentration of oxygen in the interface layer is within a range from 2times to 10 times the concentration of oxygen in each of the first andsecond polycrystalline silicon layers.
 5. The solar cell according toclaim 1, wherein the interface layer is thinner than each of the firstand second polycrystalline silicon layers.
 6. The solar cell accordingto claim 1, wherein a thickness of the interface layer is equal to orless than a thickness of the oxide layer.
 7. The solar cell according toclaim 3, wherein the concentration of oxygen in the interface layer isless than a concentration of oxygen in the oxide layer.
 8. The solarcell according to claim 1, wherein the interface layer has a thicknessof 1 nm or less.
 9. The solar cell according to claim 1, wherein theinterface layer includes a plurality of interface layers provided in theconductive area.
 10. The solar cell according to claim 1, wherein theinterface layer is in contact with the first and second polycrystallinesilicon layers that are adjacent thereto.
 11. The solar cell accordingto claim 1, wherein a dopant included in the conductive area has ahigher doping concentration than that in the single crystallinesemiconductor substrate.
 12. The solar cell according to claim 1,wherein the second surface is a front surface of the single crystallinesemiconductor substrate, and wherein the first surface is a back surfaceof the single crystalline semiconductor substrate.
 13. The solar cellaccording to claim 1, further comprising a third polycrystalline siliconlayer on the second polycrystalline silicon layer, and another interfacelayer interposed between the second polycrystalline silicon layer andthe third polycrystalline silicon layer.